The invention relates to a method for determining by capacitive means the density or total mass of rod-shaped articles dealt with by the tobacco processing industry, such as cigarettes, cigars, cigarillos, filter rods, rod-shaped streams of tobacco or other smokers' material, and other rod-shaped smoker's products. More particularly, the invention relates to the type of mass measuring method in which a high-frequency voltage is applied across the electrodes of a capacitor and the electric field lines joining the capacitor electrodes are caused to pass through the material of at least a portion of the rod-shaped article, with the effect of the mass of material penetrated by such field lines upon the capacitance of the capacitor being directly or indirectly detected to yield a measurement signal indicative of mass or density.
The invention also relates to apparatus for measuring the mass of tobacco or other material in a cigarette or other such rod-shaped article when the articles are conveyed spaced from each other along a predetermined path, and with the electric fields lines joining two electrodes of a capacitive mass or density measuring arrangement across which a high-frequency voltage is applied passing through the material of at least a predetermined portion of the rod-shaped article.
Capacitive density and mass measurement methods, due to the use of high-frequency voltages, are particularly susceptible to errors due to drift phenomena such as cause the measured value to slowly migrate, and this can lead to imprecision or to measurement errors. It is known to reduce the possibility of drift phenomena by using stabilized circuits. However, these despite their additional cost usually do not completely solve the problem.